Method for process control of mechanical embossing

ABSTRACT

Disclosed is both a method and apparatus for controlling and measuring an embossed texture on a decorative article. The embossed textured article includes both peaks and valleys that are measured and quantified to determine a profile of the textured article. Typically, the textured article comprises both chemically and mechanically embossed areas. The method uses moving average subtraction and peak/valley determinations to eliminate web flutter that often distorts the quantification of the mechanically embossed texture. The resulting profile may then be used to control a desired embossed profile.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/292,990, filed Nov. 13, 2002 now U.S. Pat.7,235,197, which is a non-provisional application claiming the benefitof Provisional Application Ser. No. 60/396,520, filed Jul. 17, 2002, thecontent of which is hereby incorporated in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for measuringand controlling a mechanical embossed texture to provide control andconsistency in embossing a texture.

BACKGROUND

Generally speaking, decorative laminates useful as surface coverings forfloors are well known in the art and have achieved broad use in bothdomestic and commercial environments. For example, decorative laminatesin the form of sheet material of a resinous polymer composition, e.g.,polyvinyl chloride, on a suitable substrate, e.g., a fibrous backingsheet, have been used for many years as sheet flooring. A goal common toall manufacturers of sheet flooring is to provide flooring productshaving appealing surface decorative effects that are both attractivefrom an aesthetic viewpoint and useful from a functional standpoint. Toillustrate, many methods and processes such as mechanical embossing,chemical embossing or inlaying have been utilized to provide contrastingsurface finishes and thereby impart decorative effects to the sheetflooring. For example, U.S. Pat. Nos. 3,000,754, 3,121,642 and 4,298,646each discloses different techniques or means for making floor-coveringproducts such as floor tiles or sheet flooring having decorative surfaceeffects.

Mechanically embossed textures often require adjusting during theprocess of forming the flooring. For example, mechanically embossedtextures may not be desirable in chemical grout lines of the flooringtile design. Thus, the mechanical texturing of the grout lines must beadjusted out of the grout lines. Presently, the human eye is used inmanufacturing lines to adjust the amount of mechanical embossing textureon vinyl sheet flooring. This subjective method is a leading cause ofvariation from run to run and operator to operator.

SUMMARY

The present invention includes both a method and apparatus for creatingan embossed textured article. The method and apparatus includequantifying a surface texture on a textured article and extracting themechanical and chemical embossing features from the random and uneventexture. The system provides for the non-subjective quantification ofsurface texture.

The method for creating an embossed textured article includesmechanically embossing a mechanically embossed texture into the articleand then quantifying the mechanically embossed texture and determining aresulting profile. The resulting profile includes the peaks and valleysof the textured article which may be formed by the embossed texture. Themechanically embossed texture is controlled or set into the texturedarticle such that the resulting profile corresponds to a predeterminedoptimum profile range.

In greater detail, the method can further include chemically embossing asurface texture onto the article and quantifying the chemically embossedsurface texture to determine a profile of the embossed textured article.Both the mechanically embossed texture and the chemically embossedtexture include valley features and peak features. Furthermore, the stepof quantifying the mechanically embossed texture and the chemicallyembossed texture includes quantifying the valley features and peakfeatures. The method can then include characterizing each valley featureand peak feature as chemically embossed or mechanically embossed andcomparing each to corresponding predetermined values to determinevalidity of each feature.

The apparatus for mechanically embossing a substrate includes a cooledembossing roller and a backup roller operatively positioned within theembossing roller such that a nip is formed between the backup roller andthe embossing roller whereby the substrate may pass through the nip andengage the embossing roller for imparting a mechanically embossedpattern. The apparatus further includes a profilometer capable ofquantifying the mechanically embossed pattern as the substrate is beingembossed.

In greater detail, the profilometer may include a laser, a computer, andanalysis software. The profilometer is capable of quantifying themechanical embossed textures and chemical embossed textures and theanalysis software is capable of differentiating between the chemicalembossed textures and the mechanical embossed textures.

In a further embodiment, the method of making an embossed articleincludes measuring the surface texture profile of the article prior tomechanically embossing the article. The method then includesmechanically embossing the article and measuring the surface textureprofile of the mechanically embossed article. The mechanically embossedtexture may then be quantified and at least one process variable may bemodified or adjusted to obtain an embossed texture profile within adesired range of textures. Such process variables can include the “wrap”time of the textured article, the nip spacing and the temperature of thetextured article.

An additional embodiment includes a method for determining a profile ofan embossed textured article having valley features and peak features.The method includes quantifying a mechanically embossed texture bydetermining an absolute depth of each valley feature and the distancebetween corresponding adjacent peak features. The method furtherincludes quantifying the chemically embossed surface texture bydetermining an absolute depth of each valley feature and the distancebetween corresponding adjacent peak features. Next, the profile of theembossed textured article is determined from the quantified data.

DRAWINGS

In the Drawings:

FIG. 1 illustrates a cross section of an embossed textured articleillustrating the mechanically and chemically embossed areas and theresulting peak features and valley features.

DETAILED DESCRIPTION

The present invention is directed to both a method and apparatus forcontrolling and measuring an embossed texture on a decorative article.The embossed textured article comprises both peaks and valleys which aremeasured and quantified to determine a profile of the textured article.Typically, the textured article comprises both chemically andmechanically embossed areas. The method uses moving average subtractionand peak/valley determinations to eliminate web flutter that oftendistorts the quantification of the mechanically embossed texture. Theresulting profile may then be used to set a desired embossed profile.

The term quantifying as used herein includes determining the number offeatures for a given distance on a textured article or surface covering.Features can be defined as the peaks and valleys found on a giventextured article. Peaks are typically defined as the high pointsrelative to the low points or valleys found on the textured article. Ingreater detail, the term quantifying can be further defined by thedisclosed algorithm wherein the peaks and valleys are determined byimplementing the first derivative over the filtered profile with thechange in slope polarity used to find peaks and valleys.

The term profile can refer to a cross-sectional view of a texturedarticle for a given distance or length of the textured article. Theprofile includes the cumulative number of peaks and valleys of a givenlength of textured article. Furthermore, the profile includes thedistance between each feature or the distances between the valleys andpeaks. Additionally, the profile includes the height of each peak andthe depth of each valley.

The predetermined optimum profile is a profile selected to give thedesired appearance of the textured article. For example, the optimumprofile may be that profile that results in the chemically embossedareas having essentially no mechanically embossed surface texture andthe remaining areas retaining the mechanically embossed surface texture.There are, of course, many such options for the predetermined optimumprofile, and the determination of such is usually that profile thatimparts the desired visual appearance upon the surface of the texturedarticle.

The term softwear filters refers to any selected technique for analyzingthe surface texture detail data and separating the selected data fromthe original data set. Software filters can include, but are not limitedto, moving average, frequency, angle, low/high/bandpass filters, andsubtraction of filtered profiles.

In greater detail, the present method includes creating an embossedtextured article by mechanically embossing a mechanically embossedtexture onto the article and quantifying the mechanically embossedtexture and determining a resulting profile. The step of quantifying themechanically embossed texture includes differentiating between achemically embossed texture and the mechanically embossed texture. Themechanically embossed texture then is controlled such that the resultingprofile corresponds to a predetermined optimum profile. Typically, themethod is continuous.

Furthermore, the method for creating an embossed textured article mayinclude both chemically and mechanically embossing a surface textureonto the article. Both the chemically and mechanically embossed areasare then quantified to determine a profile of the embossed texturedarticle. The mechanically embossed texture and the chemically embossedtexture includes valley features and peak features which also arequantified. The mechanically embossed texture then is controlled suchthat the profile of the embossed textured article corresponds to apredetermined optimum profile. Typically, the mechanically embossedtexture is controlled by cooling the textured article at a predeterminedrate to achieve the predetermined optimum profile.

The apparatus for mechanically embossing a substrate includes a cooledembossing roller and a backup roller operatively positioned with theembossing roller such that a nip is formed between the backup roller andthe embossing roller whereby the substrate may pass through the nip andengage the embossing roller for imparting a mechanically embossedpattern. A profilometer is included that is capable of quantifying themechanically embossed pattern. Any known profilometer with appropriatesensitivity may be used, including optical profilometers which include,but are not limited to, a vision system (camera, lighting, and acomputer with analysis software) or a laser and a computer with analysissoftware. The profilometer quantifies the mechanical embossed texturesand the chemical embossed textures, and the profilometer analysissoftware then differentiates between the chemically embossed texturesand mechanically embossed textures. The wrap of the substrate around aportion of the cooled embossing roller may then be adjusted such thatthe mechanically embossed texture is controlled in the substrate, withthe resulting profile of the substrate being substantially similar to anoptimized profile.

In further detail, the present method and apparatus may quantify surfacetexture on vinyl flooring using a laser profilometer and software forextracting mechanical and chemical embossing features from the random,uneven, texture. Surface textures perceived by the human eye may beobjectively quantified and the system can handle multiple (e.g., coarse,medium, fine, etc.) textures at the same time.

The software extracts chemical and mechanical surface texture depths,wall angles, and a number of associated features, and its strongcorrelation to the human eye. An important measurement is the number ofmechanically embossed features per linear distance (e.g., more featuresequals more texture to the eye). Mechanical texture is typically fineand sharp, which greatly affects gloss. Due to the profilometer'ssensitivity of 0.01 mils resolution, any movement or web flutter in theZ-axis of the web as it passes under the sensor would typically make itvery difficult to measure mechanical features accurately. Typically,this high resolution is required to measure mechanical textures. Thisproblem may be eliminated by using the moving average subtraction andpeak/valley procedures. In essence, all low frequency variation (e.g.web flutter) is ignored resulting in a very reliable on-line measurementof textures. This system can be capable of measuring the amount ofmechanical texture in a chemically restricted area (e.g., grout line)which can be important in achieving the desired visual.

For rotary mechanical embossing, the following variables can affect thedesired surface texture:

1. Proper temperature and temperature gradient of the substrate tosoften the surface to receive texture;

2. Sufficient nip pressure between embossing and backup rolls to impresstexture; and

3. Sufficient substrate cooling while in contact with embossing roll tofreeze-in the texture.

In one embodiment, variable substrate wrap around the cooled embossingroll is used to control the amount of mechanically embossed (ME)texture. With maximum wrap, the substrate can be sufficiently cooled toretain 100% of impressed texture. With zero wrap, the substrate may notbe sufficiently cooled and most, if not all, impressed texture cancompletely fade away. Essentially, wrap controls the amount of texturefade-away.

The adjustment of the wrap is a fast and simple way to control texturefor rotary mechanical embossing (ME) on vinyl sheet flooring. Withaccurate on-line texture measurement as feedback, the wrap control canbe automated to insure consistent mechanical texture from run to run.Variable wrap control can be used on any rotary ME process that requiressubstrate cooling to freeze-in the image. An example of an apparatuscapable for use in mechanically embossing a substrate can be found inU.S. Pat. No. 4,142,849, which is incorporated herein in its entirety.

The advantages of using variable wrap for texture control include quickcontrol and immediate response to wrap change. Also, fine control ispossible since large wrap changes can cause small texture change.Furthermore, 100% control and maximum texture to zero texture ispossible depending upon process conditions.

In one embodiment, texture control can provide the ability to remove MEtexture in the CE restricted areas. With the amount of wrap properlyadjusted, ME texture impressed in the restricted areas canrecover/rebound without major loss of texture in the unrestricted area.

Texture Measurement Hardware:

The texture measurement system consists of a laser profilometer (e.g.,LMI Laser twin sensor, Model LTS 15/1) capable of measuring depth (i.e.,distance from a surface to the laser head) with 0.00001-inch resolutionwith a spot size of 0.001″ at a frequency up to 100 kHz. The analogoutput of the profilometer sensor and linear displacement encoder areinputs to a high-speed data acquisition system, such as the SciemetricModel 270 Process Verification System, that records depth measurementsevery 0.002″ of linear movement of the target. This provides thenecessary surface profile data to be analyzed by the following featureextraction software.

Texture Measurement Software:

To extract and measure CE and ME features, the following process can beimplemented in Excel, Visual Basic, or Sciemetric Inspexion software.

For CE Extraction:

Apply low pass filter to profile data. This can be done by using amoving average to smooth and eliminate all ME data. Also, commonly usedButterworth and Bessel filters can be applied.

For ME Extraction:

Apply high pass filter to profile data. This can be done by subtractingthe original profile data from a moving average profile to eliminate allCE data. Also, commonly used Butterworth and Bessel filters can beapplied.

-   -   The following is applied for both CE and ME measurements:    -   1. Find all the peaks and valleys by implementing the first        derivative over the filtered profile. A change in slope polarity        can be used to find peaks and valleys effectively;    -   2. Calculate all peak/valley and valley/ peak depths;    -   3. Calculate all peak/valleys and valley/peaks linear sizes;    -   4. Validate CE/ME features (i.e., minimum and maximum depths and        sizes);    -   5. Calculate average, maximum, and minimum depths and angles;        and    -   6. Count number of CE and ME features per linear distance (i.e.        feature frequency).        ME Texture Control:

The average of 30 or more ME feature count provides a reliablemeasurement of ME texture. The texture error (i.e., measuredtexture−setpoint texture) is removed by automatically adjusting theposition of the embosser wrap roll and changing the amount of substratewrap around the embossing roll. Electrical, pneumatic, hydraulic servoscan be used for wrap roll position control.

Surface Texture Measurement System for Vinyl Sheet Flooring

Description of Vinyl Floor Texture:

Surface texture in vinyl sheet flooring can be produced chemically, forexample, by selectively restricting the expansion of the foamable(bottom) layer and mechanically by pressing a texture into the clearwear (top) layer. Chemical texture is generally deeper, larger, and lesssharp than mechanical texture. An example of chemical texture is a groutarea around a ceramic tile pattern. An example of mechanical texture isthe fine wood ticking found in real wood grain. These textures, as theyoccur naturally, vary in shape, size, and distribution.

General Chemical Embossed (CE) Texture Characteristics Used in CurrentFlooring Products:

Depth: about 5 to 25 mils

Width: about 30 to 500 mils

Wall Angle (angle relative to surface): about 5 to 20 degrees

Frequency: about 0 to 5 features per 1 inch

General Mechanical Embossed (ME) Texture Characteristics Used in CurrentFlooring Products:

Depth: about 0.5 to 4 mils

Width: about 5 to 15 mils

Wall Angle (angle relative to surface): about 5 to 40 degrees

Frequency: about 10 to 50 features per 1 inch

Description of Measurement System:

Three fixed measurement points across a moving 12′ wide sheet may beused to measure surface texture at the center and edges of the sheet. Anincremental encoder will provide linear displacement of the sheet with aresolution on 0.0024″/pulse. Profiles may be taken every 5 feet of sheettravel for 2.45″ (i.e., 1024 data points). At a line speed of 150 fpm, anew set of measurements will occur once every 2 seconds. Algorithmsbelow may be applied to extract ten measurements from each of the threeprofiles for a total of 30 measurements. Each of the 30 measurements maybe averaged over 10-30 profile sets before sending to an Allen BradleyPLC via DeviceNet or Data Highway. The PLC will provide a signal toenable/disable measurements.

Algorithm for Chemical Embossing:

-   -   Normalize the profile data by subtracting the profile average        from each point.    -   Calculate a moving average at each point (e.g., the average of        10 points before and after).    -   Calculate the slope for each (moving average) point.    -   Determine peaks and valleys via slope/polarity change.    -   Calculate absolute value of depths by subtracting all        peak/valley and valley/peak features.    -   Calculate run (i.e., distance from peak/valley and valley/peak)        for each features.    -   Determine if feature meets criteria for chemical feature (i.e.        min/max depth & run).

Calculate wall angle for each valid peak/valley and valley/peak usingdepth and run info.

Final Measurements

-   -   Calculate average of depths and angles.    -   Determine maximum depth and angle.    -   Count number of valid chemical features.        Algorithm for Mechanical Embossing:    -   Normalize the sample data by subtracting each point from each        moving-average point.    -   Calculate the slope for each point.    -   Determine peaks and valleys via slope/polarity change.

Calculate absolute value of depths by subtracting all peak/valley andvalley/peak features.

-   -   Calculate run (i.e., distance from peak/valley and valley/peak)        for each features.    -   Determine if feature meets criteria for mechanical feature (i.e.        min/max depth & run).    -   Calculate angle for each valid peak/valley and valley/peak using        depth and run info.        Final Measurements    -   Calculate average depths and angles.    -   Determine maximum depth and angle.    -   Count number of valid mechanical features.        Parameters for System Configuration:    -   Interval for moving average (number of points)    -   Linear resolution in mils (encoder resolution)    -   CE minimum rise in mils (must be > to be valid CE)    -   CE maximum rise in mils (must be < to be valid CE)    -   CE minimum run in mils (must be > to be valid CE)    -   CE maximum run in mils (must be < to be valid CE)    -   ME minimum rise in mils (must be > to be valid ME)    -   ME maximum rise in mils (must be < to be valid ME)    -   ME minimum run in mils (must be > to be valid ME)    -   ME maximum run in mils (must be < to be valid ME)    -   Number of profile measurements to average    -   Minimum number of valid CE features (fewer features=no CE)    -   Minimum number of valid ME feature (fewer features=no ME)

While Applicants have set forth embodiments as illustrated and describedabove, it is recognized that variations may be made with respect todisclosed embodiments. Therefore, while the invention has been disclosedin various forms only, it will be obvious to those skilled in the artthat many additions, deletions and modifications can be made withoutdeparting from the spirit and scope of this invention, and no unduelimits should be imposed except as set forth in the following claims.

1. A method for making an embossed article comprising: mechanicallyembossing a surface of the article; non-subjectively quantifying themechanically embossed surface of the article with a profilometer andanalysis software as the article is being mechanically embossed bydetermining (a) the profile of individual valley features and peakfeatures or (b) the depth of an individual valley feature and thedistance between the valley feature and an adjacent peak feature; usingthe quantified mechanical embossing to control the mechanical embossingdepth as the article is being mechanically embossed; measuring a surfaceprofile of the mechanically embossed article as the article is beingmechanically embossed: and adjusting at least one process variable asthe article is being mechanically embossed to obtain an embossed profilewithin a predetermined range of embossed profiles, wherein the surfaceprofile of the article is measured prior to mechanically embossing thearticle and non-subjectively quantifying the mechanically embossingincludes subtracting the profile measured prior to mechanicallyembossing the article from the profile measured after embossing as thearticle is being embossed.
 2. The method of claim 1, further comprising:chemically embossing a surface of the article; and non-subjectivelyquantifying the chemically embossed surface of the article with aprofilometer and analysis software as the article is being chemicallyembossed by determining (a) the profile of individual valley featuresand peak features or (b) the depth of an individual valley feature andthe distance between the valley feature and an adjacent peak feature. 3.The method of claim 2, wherein the steps of non-subjectively quantifyingthe mechanical embossing and the chemical embossing includesnon-subjectively characterizing individual valley features and peakfeatures as chemical embossing or mechanical embossing as the article isbeing embossed.
 4. The method of claim 3, wherein the characterizationincludes comparing the quantified valley features and peak features,including the depth of an valley feature and the distance between thevalley feature and an adjacent peak feature, to predetermined valueranges as the article is being embossed.
 5. The method of claim 1,wherein the step of controlling the mechanical embossing depth includeswrapping the article around a portion of a cooled embossing roll andadjusting the wrap around the embossing roll as the article is beingembossed.
 6. The method of claim 2, wherein the step of quantifying themechanically embossed surface includes differentiating between thechemically embossed features and mechanically embossed features as thearticle is being embossed.
 7. The method of claim 2, wherein the step ofcontrolling the mechanical embossing depth includes wrapping the articlearound a portion of a cooled embossing roll and adjusting the wraparound the embossing roll as the article is being embossed.
 8. Themethod of claim 1, wherein the method further includes non-subjectivelycharacterizing valley features and peak features, wherein thecharacterization includes comparing the quantified valley features andpeak features to predetermined value ranges as the article is beingmechanically embossed.
 9. The method of claim 1, wherein adjusting theat least one process variable includes wrapping the article around anembossing roll and adjusting the wrap around the embossing roll as thearticle is being embossed.
 10. The method of claim 1, wherein the methodincludes mechanically embossing the article by passing the articlethrough a gap and adjusting the gap setting as the article is beingembossed.
 11. A method of measuring and controlling a mechanicalembossed profile into a chemically embossed article comprising:measuring the surface profile of the chemically embossed article priorto mechanically embossing the article; mechanically embossing thearticle; measuring the surface profile of the mechanically embossedarticle as the article is being mechanically embossed; non-subjectivelyquantifying the mechanical embossing as the article is beingmechanically embossed by determining (a) the profile of individualvalley features and peak features or (b) the depth of an individualvalley feature and the distance between the valley feature and anadjacent peak feature; and adjusting a process variable as the articleis being mechanically embossed to obtain a desired mechanical embossingprofile.
 12. The method of claim 11, wherein the non-subjectivelyquantifying is accomplished by computer analysis of the measured surfaceprofile, the computer analysis differentiating between chemicalembossing and mechanical embossing as the article is being embossed. 13.The method of claim 11, wherein non-subjectively quantifying themechanically embossed texture includes subtracting the profile measuredprior to mechanically embossing the article from the profile measuredafter embossing as the article is being embossed.
 14. The method ofclaim 11, wherein the step of non-subjectively quantifying themechanical embossing comprises analyzing the output of a profilometerwith analysis software as the article is being embossed.